They should be 3x1 (or 1x3), which means middle and sides so I can make bench of any length in map editor, should have all directions (back/front/left/right) and should look nice with standard VX Ace RTP graphics (or VX RTP, as both are as similar as VX and Ace themselves are similar to each other).
//edit: Not relevant anymore as Ayene made benches for me: